Process for soil stabilization

ABSTRACT

Soil is treated by contacting it with a slurry of high absorbency alkali metal silicate in a non-aqueous fluid and reacting the silicate with an alkali metal acid phosphate or an amide having the formula   wherein R is hydrogen, an alkyl group having one to four carbon atoms, an alkoxy group having one to four carbon atoms or -CONX2 wherein X is hydrogen or an alkyl group having one to four carbon atoms in the presence of from 1 to 2.5 moles of water per mole of alkali metal oxide in the silicate.

DeVries 1 1 Sept. 30, 1975 [54] PROCESS FOR SOIL STABILIZATION 3.583.1666/1971 Gruf et a1 v. 61/36 R [75] lnventor: Frederick William DeVries,Chadds Ford Pa. Prunary Examiner-Stephen J. Novosad [73] Assignee: E. l.Du Pont de Nemours and [57] ABSTRACT Company, Wilmington. Del. Soil 15treated by contacting it with a slurry of high ab- [22] Flled: 1974sorbency alkali metaLsiljcatc in a non-aqueous fluid [2 11 APP] NOJ461732 and reacting the silicate with an alkali metal acid phosphate oran amide having the formu a r [52] US. Cl 61/36 R; 166/292; 106/74 [51]Int. Cl.'-. E02D 3/12: E02D 3/14; E218 33/138 0 [581 Field 61 Search166/292-294, g 166/300; 61/36 R, 35; 106/74 [56] References Cited f\vhereinbR is hydrogen, an alkyl grcaup having one to our car on atoms,an alkoxy group aving one to four UNITED STATES PATENTS carbon atoms orCONX. wherein X is hydrogen or 2.968.572 1/1961 Peeler. .Ir. 61/36 R analky] group having one to f Carbon moms in the presence of from 1 to 2.5moles of water per mole of r 1 I 3.288.040 11/1966 Burrows 61/36 R x mthe 3.558.506 1/1971 Bonncl et ul 61/36 R 10 c N Drawings PROCESS FORSOIL STABILIZATION BACKGROUND OF THE INVENTION Various methods, bothchemical and non-chemical, have been employed in an attempt to stabilizethe substrate from which oil is produced. Particularly with respect tosand formations, the aim is to stabilize the loose sand in the depositwhile maintaining the permeability of the sand to the flow of oil.

In the old gravel pack technique, larger particles of gravel weredeposited around the base hole and the sand was allowed to pack aroundit. The problem with such a solution remained the difficulty in gettingthe gravel adequately arranged in the base hole and the criticality indetermining exactly the proper size of the gravel to be used. If thegravel was too coarse, the sand still escaped into the oil. If thegravel was too fine, the sand packed and a high pressure drop would beset up around the pack.

Many chemical methods for combatting this problem have been proposed,and the process described in U.S. Pat. No. 2,968,572 issued on Jan. 17,1961 to Cletus E. Peeler is the currently employed technique. While thismethod can be used to stabilize sand formations, it suffers thedisadvantage of yielding an essentially oil impermeable structure.

SUMMARY OF THE INVENTION It has now been found that unstable soilformations, particularly sand formations, can be stabilized while oilpermeability is maintained when the soil is treated with a slurry ofhighly absorbent, low bulk density, hydrated alkali metal silicate in anon-aqueous fluid and the silicate is reacted while in intimate contactwith the formation, with an amide having the structure wherein R ishydrogen, an alkyl group having one to four carbon atoms, an alkoxygroup containing one to four carbon atoms or CONX wherein X is hydrogenor an alkyl group having one to four carbon atoms or an alkali metalacid phosphate or a mixture of any of them in the presence of water. Ifdesired, a reactive additive may be used to speed up theinsolubilization of the silicate in the soil.

DETAILED DESCRIPTION OF THE INVENTION The most critical element involvedin achieving sta bility coupled with permeability in accordance withthis invention is the unique silicate employed in the form of a slurryin a non-aqueous fluid. Specifically, the alkali metal silicates arespheroidal, amorphous and have a mole ratio of SiO to alkali metal oxideof 1 to 3.75. The silicates of the invention are characterized by a bulkdensity of less than 0.5 g./cc. and a maximum water content of 30% byweight. They also have a spe cific nitrogen surface area between 2.5 and7 m.'-/g. The alkali metal silicates include silicates of sodium,potassium, lithium, rubidium, cesium and mixtures thereof. Sodiumsilicates are preferred.

Any alkali metal silicate having the above characteristics may be used.One such suitable material is made by contacting essentially discretealkali metal silicate particles with aqueous solutions of hydrogenperoxide,

absorbing the peroxide into the alkali metal silicate hydrated structureand heating the silicate to destroy substantially all of the hydrogenperoxide, thereby causing the silicate to swell and form a high surfacearea aggregated structure having an extremely high absorbency. Thesetypes of silicates and the methods by which they are prepared arediscussed in detail in US. application Ser. No. 425,970 filed Dec. 19,1973.

It is important that the silicate be in place in the formation to bestabilized before the insolubilization of the silicate takes place viareaction with the acid phosphate or amide. Generally the silicate ispumped into the formation after it is slurried in a non-aqueous fluid.The concentration of the silicate in the slurry is not critical as longas the slurry is sufficiently fluid to be pumped into the soil to betreated. Generally, 10 to 30 and preferably 20 parts by volume ofsilicate per parts by volume of the non-aqueous fluid are suitable.

Any non-aqueous fluid which is inert to the silicate and the acidphosphate, amide or reactive salt used may be employed, including a gas,as long as the fluid is a liquid at the temperature, pressure, porosityand other conditions prevailing in the soil to be treated. Generallysuitable material would include linear, branched, cyclic, aromatic,aliphatic, saturated or unsaturated hydrocarbons and oxygen-containinghydrocarbons such as epoxides, ketones, alcohols and the like ormixtures of any of them, preferably containing 3 to 20 carbon atoms. Thenon-aqueous fluid should be inert with respect to the silicate, amide,acid phosphate and any reactive additive used. Specific examples of somesuitable materials include the crude oil from the well or any otherinert petroleum product or cut, petroleum naphtha, hydrocarbons,liquified petroleum gas, petroleum ether, methanol, benzene, toluene,xylene, diphenyl ether, diisobutyl ketone, biphenyl, cyclopentane,hexadiene, cyclohexane, 4-ethyl-5 methyl octane, eicosane and the likeand mixtures of any of them, particularly mixtures of benzene, tolueneand xylene.

The volume of the silicate that should be used depends on the verticalinterval of the formation and the distance out into the formation awayfrom the well that it is desired to treat. Treatment volume depends onfactors such as porosity and surface area. Normally, one volume ofsilicate per volume of pore space is adequate. In some cases, less ofthe silicate will protect considerably more pore space. Since thecharacteristics of soils vary, different treatment volumes will berequired depending on soil conditions. Generally, however, it ispreferred to inject from 1 to 0.15 volume of silicate per pore volume ofthe soil to be treated.

Any amide having the formula as defined herein or mixtures thereof maybe used. Some such suitable amides include,- for example, formamide,acetamide, propionamide, butyramide and N- substituted derivatives suchas N-methyl formamide, N,N-dimethyl formamide, N-monoand diethylformamide and the like. Formamide is preferred. Any alkali metal acidphosphate may also be used including sodium, potassium, lithium, cesium,rubidium, and the like acid phosphates, acid pyrophosphates and thelike.

The amide and/or acid phosphate and silicate can be so proportioned asto provide insolubilization of the silicate within one-half to eighthours at the temperature of the soil, generally from C. to 250C.Ideally, the amount of amide to be used varies from 0.2 to 1.5,preferably 0.3 to 0.6, acid equivalents derived via hydrolysis of theamide per equivalent of alkali metal oxide in the silicate at thereaction site. If an acid phosphate is used, the same equivalency at thereaction site based on the acid hydrogen content of the phosphate isused. Any excess amount of the amide and/or phosphate may be used toinsure that the specified amount of these materials is available at thereaction site to completely react the silicate.

No reactive salt need be employed unless a high degree of initial gelwater insolubility is desired. Any amount of the reactive salt may beused but, because the insolubilized structure would be brittle ifreactive salt alone were used to insolubilize the silicate, it ispreferred that amounts up to a maximum of 80% of equivalency beemployed. Thus, from 0 to 80% of the equivalent amount of the reactivesalt needed to react completely with the silicate is preferably presentat the reaction site. Any salt reacm' e .to insolubilize the silicatemay be employed including, for examp e, sodium aluminate, sodiumbicarbonate, ferric chloride, aluminum chloride, cupric sulfate, cupricchloride, zinc chloride, calcium chloride and the like and mixturesthereof.

The amide or acid phosphates or mixtures thereof may be introduced tothe silicate after the slurry is pumped into the formation, or they maybe slurried in the nonaqueous medium with the silicate. Any acidphosphate or amide such as formamide, which is a liquid at welltemperatures and pressures may be added separately. The amide or acidphosphate may also be dissolved in the additional water and pumped tothe silicate slurry already in place in the formation. Although thelatter mode of introduction is preferred, any desired method may be usedto introduce the amide or acid phosphate to the silicate. Because thevolume of amide or acid phosphate and water is small, use of this lattermethod may require the addition of an excess of these agents to assurethe presence of the proper amounts at the reaction site, the location ofthe silicate particles.

The amount of water required at the reaction site is, at most, thestoichiometrically equivalent amount necessary to hydrolyze the silicateto silica and achieve dissociation of the amide or dissolution of theacid phosphate. Overall, from 0.8 to 2.5 moles of alkali e ide isilicate at the reaction site is adequate. When an amide is used, from 1to 2.5 moles of water should be present at the reaction site per mole ofalkali metal oxide in the silicate, and preferably 1.8 t of water areemployed. This amount is adequate to hydrolyze the amide and thesilicate. When an acid phosphate is used, from 0.8 to 1.2

- moles of water should be present at the reaction site per mole ofalkali metal oxide in the silicate. Since the acid phosphate does nothydrolyze but merely dissolves in the water, less water is consumed whenan acid phos phate is employed.

The water can be added to the silicate in the formation after or withthe amide or with the acid phosphate. When an amide is used, the watercan also be mixed into the initial silicate slurry. When an acidphosphate is used, the water is preferably used to dissolve thephosphate so that the phosphate can react. In this instance, the wateris introduced as a solution of the phosphate. The water may also beadded to the nonaqueous slurry of the silicate. If the amide or acidphosphate is also to be added to the slurry of the silicate in anon-aqueous fluid, the precise amounts of the water and the amide oracid phosphate must be employed to allow an adequate time period withinwhich the composition can be pumped into the soil to be treated beforereaction starts. If sufficient water is present in the formation, noadditional water need be added. If some water is present but it is notsufficient for the reaction of this invention, supplementary portions ofwater may be added. The source of the water is irrelevant as long as anadequate amount is available to the amide or acid phosphate andsilicate.

The invention is further illustrated but is not intended to be limitedby the following examples.

EXAMPLE 1 A slurry is constituted as follows: 20 parts by volume (about4 grams) of a high-absorbency im gntainin 7 0 0.2.4 SiO and 25% water, 1part by volume fogmamide (about 1 gram), 1 part by volume water (about 1gram), 100 parts by volume of a naphtha cut averaging C H, (aboutgrams). This slurry is pumped at 25C. into a loose sand formation, to avolume four times the porosity of the sand. The sand acts to filter outand entrap the silicate particles. The silicate is insolubilized inabout 8 hours leaving a stable structure still permeable to oil.

EXAMPLE 2 A slurry comprising 20 parts by volume of ahighabsorbencysiligate, bulk density 0.15 gram per cc. and conta' ingabout 207 mbined w r, in volumes ethanol 18 pumped at 25C. through aporous, loose sand formation, to a level twice that of the porosity ofthe sand. 20 Volumes of a 70:30 mixture of formamidezwater are pumpedthrough the formation. This is an excess quantity used to insure asufficient quantity of water and formamide at the reaction site. Astable structure is formed within an hour. The formation is permeable tooil.

EXAMPLE 3 The slurry described in Example 1, excluding the water, usingthe method outlined in Example 1, is pumped at 25C. into a sandformation already wet with ground water. An assay of the drained sandshows the presence of at least one part of water per parts of slurry.The silicate sets up in about 8 hours as in Example 1.

EXAMPLE 4 The slurry of Example 1 except that it contains 0.5 part byvolume of formamide and no water is pumped at 25C. into a loose sandformation wet with a 5% solution of calcium chloride in water at avolume four times the porosity of the sand. The drained sand contains atleast 5 parts by volume of solution per 120 volumes of slurry. Gellationoccurs within 4 hours, to leave a stable, oil-permeable formation.

EXAMPLE 5 A slurry comprising 20 parts by volume of the silicate ofExample 1, 100 parts by volume of toluene, 0.5 part by volume offormamide, and 1 part by volume of water is pumped at 100C. into a loosesand formation at a volume four times the porosity of the sand. Gellingoccurs within an hour, with additional curing occurring during 8additional hours at this temperature as evidenced by increasingstability. The formation remains permeable to oil.

EXAMPLE 6 A slurry comprising parts by volume of a (12.4)high-absorbency potassium silicate, with a bulk density of 0.2 gram percc. and a water content of 20%, and 100 parts by volume of cyclohexaneis pumped into a porous, loose sand formation at 50C. to the extent of 3volumes slurry per volume pore opening in the sand. A solutioncontaining 20 parts by weight of sodium acid pyrophosphate per 100 partsby weight of water is pumped at 50C. through the sand to a level ofthreefourths the pore volume of the sand. Silicate is gelled within onehour and develops increased strength through curing over the next 12hours to yield a stable, oil-permeable structure.

EXAMPLE 7 The slurry described in Example 6 is pumped, at the samevolume, into a porous, loose sand formation containing 1.5% by volumeferric chloride per pore volume. The solution of sodium acidpyrophosphate described in Example 6 is pumped through at a level ofone-half the pore volume of the sand. The silicate is gelled within onehour and it develops increased strength during the next 6 hours yieldinga stable, oilpermeable formation.

EXAMPLE 8 The slurry described in Example 1 except that two parts ofdimethylformamide are substituted for the one part formamide, is pumpedinto a porous sand formation under the same conditions as described inExample 1. The impregnated sand is then subjected in a bomb to atemperature of 200C, thus simulating conditions at the base of an oilwell. The bomb maintains the developed pressure of the water anddimethylformamide so that vapors cannot escape from the sand. Thestructure becomes stable within 24 hours and remains oilpermeable.

While the invention has been described in considerable detail in theforegoing, it is to be understood that such detail is solely for thepurpose of illustration and that variations can be made by those skilledin the art without departing from the spirit and scope of the inventionexcept as set forth in the claims.

What is claimed is:

1. An improved method for treating soil which comprises contacting thesoil with a slurry of highly absorbent, low bulk density, hydratedalkali metal silicate in a non-aqueous fluid and reacting an alkalimetal acid phosphate or an amide of the formula wherein R is hydrogen,an alkyl group having one to four carbon atoms, an alkoxy group havingone to four carbon atoms, or -CONX wherein X is hydrogen or an alkylgroup having one to four carbon atoms and from O to of the equivalentamount of a reactive salt with the silicate in the presence of from 0.8to 2.5 moles of water per mole of alkali metal oxide in the silicate.

2. The method of claim 1 wherein the alkali metal silicate is sodiumsilicate.

3. The method of claim 1 wherein the silicate has a ratio of silicondioxide to alkali metal oxide of l to 3.75, a bulk density of less than0.5 g./cc. and a maximum water content of 30%.

4. The method of claim 1 wherein the silicate is reacted with formamide.

5. The method of claim 1 wherein the silicate slurry is pumped into thesoil and the acid phosphate or amide, dissolved in the water, is pumpedinto soil containing the silicate.

6. The method of claim 1 wherein the acid phosphate or amide is slurriedwith the silicate, pumped into the soil and the water is introduced intothe soil containing the acid phosphate or amide and silicate.

7. The method of claim 1 wherein the silicate is reacted with an amidein the presence of 1.8 to 2.2 moles of water per mole of alkali metaloxide in the silicate.

8. The method of claim 1 wherein the silicate is reacted with an acidphosphate in the presence of 0.8 to 1.2 moles of water per mole ofalkali metal oxide in the silicate.

9. The method of claim 1 wherein the amide or acid phosphate provides0.2 to 1.5 acid equivalents per equivalent of alkali metal oxide in thesilicate.

10. The method of claim 1 wherein the non-aqueous fluid is a linear,branched, cyclic, aromatic, aliphatic, saturated or unsaturatedhydrocarbon or oxygencontaining hydrocarbon having 3 to 20 carbon atoms.k I!

1. AN IMPROVED METHOD FOR TREATING SOIL WHICH COMPRISES CONTACTING THESOIL WITH A SLURRY OF HIGHLY ABSORBENT, LOW BULK DENSITY, HYDRATEDALKALI METAL SILICATE IN A NON-AQUEOUS FLUID AND REACTING AN ALKALIMETAL ACID PHOSPHATE OR AN AMIDE OF THE FORMULA
 2. The method of claim 1wherein the alkali metal silicate is sodium silicate.
 3. The method ofclaim 1 wherein the silicate has a ratio of silicon dioxide to alkalimetal oxide of 1 to 3.75, a bulk density of less than 0.5 g./cc. and amaximum water content of 30%.
 4. The method of claim 1 wherein thesilicate is reacted with formamide.
 5. The method of claim 1 wherein thesilicate slurry is pumped into the soil and the acid phosphate or amide,dissolved in the water, is pumped into soil containing the silicate. 6.The method of claim 1 wherein the acid phosphate or amide is slurriedwith the silicate, pumped into the soil and the water is introduced intothe soil containing the acid phosphate or amide and silicate.
 7. Themethod of claim 1 wherein the silicate is reacted with an amide in thepresence of 1.8 to 2.2 moles of water per mole of alkali metal oxide inthe silicate.
 8. The method of claim 1 wherein the silicate is reactedwith an acid phosphate in the presence of 0.8 to 1.2 moles of water permole of alkali metal oxide in the silicate.
 9. The method of claim 1wherein the amide or acid phosphate provides 0.2 to 1.5 acid equivalentsper equivalent of alkali metal oxide in the silicate.
 10. The method ofclaim 1 wherein the non-aqueous fluid is a linear, branched, cyclic,aromatic, aliphatic, saturated or unsaturated hydrocarbon oroxygen-containing hydrocarbon having 3 to 20 carbon atoms.